I agree that the sibiling-like relationship exists between A&R due
to the fact that they were living under the same roof.  However, there
is evidence that their relationship was something more.  In v36, when
Akane found out that Ranma was imitating Nadoka, she didn't quarrel with
him because they can only see each other at school and they were not
living under the same roof (p. 146-7, correct me if I'm wrong about the
translation).  Now the sibiling-relationship is not as strong, we can
see that there was something more in their relationship because they
wanted to make up with each other.  I think my arguement is a little too
weak... bear with me...

    But I think that the sibiling relationship dominates the love
relationship throughout the whole series, especially in the beginning. 
Anyone agree with me ?  Disagree?